Personal Digital Assistants (PDA) are microprocessor-based computers that emphasise their small size and personal information management capabilities. Conventional PDAs utilise a single screen. The PDA screen surfaces are touch sensitive to permit input functions. One screen is usually provided, the small size of which results in a limited input and output-working surface. Multiple screens can increase the user's effective, or virtual, screen real estate.
Electronic books are known to provide multiple screens (U.S. Pat. No. 5,534,888 to Lebby et al., U.S. Pat. No. 5,467,102 to Kuno et al., and U.S. Pat. No. 5,239,665 to Tsuchiya). Multiple screens are known which can display a single virtual (or linked) image (Kuno). In U.S. Pat. No. 5,579,481 to Drerup, networked computers use a wireless stylus and standard CRT screens to enable files to be moved from one networked computer to the other through application of the stylus to the screen. The stylus has an identifier and when applied to screen A, the selected file is associated with the unique ID of the stylus. Later, if the stylus is applied to a second screen B, the computer for screen B recognizes the ID of the stylus, remembers the file associated with it and then retrieves the file through the network from the computer associated with screen A.
Note however, that this approach to maintaining continuity is not feasible for Personal Digital Assistants that have more than one touch screen.
As described in greater detail below, known input devices include touch screens, touchpads and digitizers. All use basically the same grid construction to sense the co-ordinates of the user's input through a pointing device, be it a stylus or fingertip.
Touch screen displays have been introduced and widely used due to their intuitive interface and low-cost. Computers with touch-screen displays regard the operator's fingers or a hand-held stylus as the pointing device that manipulates the display's surface.
Computers with multi-displays are known where the nature of the application requires greater screen real estate (e.g., CAD applications) or the ability to have multiple entry points (e.g., machine-code debuggers). Typically these computers use standard pointing devices like a mouse or a digitizer for input.
Standard pointing devices utilize a flat, continuous surface which software maps to the displays' real estate. Through software, the displays are mapped either to a single virtual desktop or to multiple desktops. The pointing device moves continuously through the entire virtual desktop.
Where multiple displays underlie a discontinuous -display surface, through the pointing device, users can drag, transfer and manipulate objects across the multiple displays because the pointing device itself never crosses a discontinuity in the input surface.
Computers with multi-displays that employ touch screen technology will have the displays' surfaces functioning as the `pointing device surfaces`. There is a complexity in building intuitive user interfaces if the displays were mapped to a single virtual desktop and the user needs to move and manipulate objects across the multiple displays. This complexity results from the fact that there is a physical discontinuity in the `pointing device surfaces`.
Multiple screens, which are capable of displaying a single virtual image, and which also will allow touch-screen input, are not known to the applicants. This is further complicated in the situation where, in graphical user interfaces (GUI), it is common to select an object (e.g. an icon representing a file, a text or graphic clip, etc.) and drag it to a specific location on the screen (e.g. a "trashbin" icon for deleting the file). With a single, continuous screen, which doubles as an input surface, a user may easily identify or select the object by touching it with a pointing implement or device. Then in a continuous movement the user may drag the object across the surface of the display (maintaining contact between screen and the pointing device) and release the object once there for whatever purpose. However, as stated, with multiple screens, there is necessarily a physical discontinuity therebetween. Thus, one cannot maintain this continuous movement of the stylus without losing contact between the screen and stylus and accordingly lose the object when crossing the discontinuity.